Pilot-channel-indicating system



1,642,710 Sept. 20, 1927. H. A. AFFEL PILOT CHANNEL INDICATING SYSTEM Filed sepff 18, 192e 2 sheets-sheet 1 IN VEN TOR ATTORNEY e t. 20 1927. S p H. A. AFFEI.

PILOT CHANNEL INDIATING SYSTEM 2 Sheets-Sheet Filed Sept. 18, 1926 IN VEN TOR Edf/Q7@ ff @gri ATTORNEY c L L Patented sept. ze, rear.,

- i 'lhtlllt erica.

'HERMAN A. AFFEL, 0F RIJDG'EWOQD, NEW JERSEY, ASSGNOR TO AMERIICAN TEL- PHONE AND TVELEGRAPH- COMPANY, .A CORPORATION-OF NEW YORK.

' PILOT-CHANNEL-INDICATING SYSTEM Application filed September 18, 1926. Serial No. 136,261.

' This inventiony relates to pilot channel alarm arrangements for use in connection with carrier or radio signaling systems, and particularly to means connectedwith such systems wherebythe location of a source of trouble upon the system aecting its transmission characteristics willbe automatically made known at one or more places thereon.V

ln the operation of carrier and radio signaling systems employing one or more repeaters between the terminals thereof, it is customary to transmit a single frequency wave'together with the signaling waves, the single frequency wave being known as a pilot l5 channel. The pilot channel serves as an index of line conditions 'that affect the transmission* of signals. The frequency of the pilot channel is so lchosen with respect-to the frequency of the signaling waves that Aany 2@ variation of line conditions that a'ect it will,

in like manner, affecty the signaling channels being transmitted over the line simultaneg ously with the pilot channel. J

Heretofore in order todetermine line conditions and to locate assource of trouble it has been customary to select the pilot frequency at each repeater station and also at the receiving terminal station, and to impress it upon `suitable circuits whereby its 3@ variations from normal would be indicated. Thus each repeater point has been equipped i with an alarm circuit which would operate whenever the pilot channehvari'ed in voltage a given amount above or below normal. vThe Vrepeater attendant would measure the varia- J' tion and would notify the attendant atthe receiving terminal station, to whom is assigned the duty of supervising the operation of the line and of directing the various repeater attendants, to make such adjustments upon the line at such repeater stations as are necessary to bring the transmission back to normal. 'This requires the repeater attendants to notify the attendant at the terminal station whenever variations occur, and inform him of the magnitude of such varia-- tions, all. of which introduces a loss of time in eecting the necessary adjustments to bring the transmission to normal.

This invention resides lin a method and means whereby abnormal variations ofthe transmission level of the pilot channel at each repeater point are automatically made known to the attendant at a terminal station. @ther objects of this invention will be apparent from the following description when. read in connection with theV attached drawing, of which Figure l shows schematically a simple form of embodiment of the invention; Fig. 2 shows schematically the manner in whichthe apparatus is connected into a carrier transmission system; and ltig. 3 shows another form ot the invention containing certain retinement-s not shown in Fig. l.

ln'Fig. l, the line L1 represents one of the branches at a repeater station as shown in Fig. 2, into which the line L, divides. The repeater lt, is intended to amplify all of the frequencies transmitted in the direction of the arrow which include not only the signaling channels but also the pilot channel. Bridged across the :output side of the repeater is a pilot alarm circuit by'means of which the attendant at a terminal station may receive automatically an indication of the line condition, which indication will be produced by the pilot channel. rllhe conductors of thev pilot alarm circuit which are bridged across the output side of the repeater are connected with the primary winding of the transformer 1, which winding has in series therewith a condenser 2 which together form a circuit tuned to the pilot channel frequency. The secondary winding is connect- 3. This winding has connected across it a" condenser 4 which tunes the input circuit of the rectilier to the pilot channel frequency. The output side of the rectifier includes the Winding' of the relay 5 and a meter 6. 'The armature of `this relay has connected therewith a source of potential 7, which, when the `relay is operated, willbe connected with a local alarm signal 8 and with the relays 9 and 10. Relay 9 serves to connect a source'of power 11 with the motor 12 which drives a commutator 13 by means of which the output of the oscillator 14 will be transmitted over the line L, in accordance with a predetermined code. This oscillator may be of any well-knowntype, so that a detailed explanation of it is unnecessary. Since a desirable, form is a vacuum. tube type, the relay 9 could J rk V 1 ed with the grid of the vacuum tube rectifier oscillations 14 and with the output of the' repeater R, through the anti-resonant cir- 'at its midposition. fthe amplitude of the carrier frequency be-Av came greater or tor A the oscillator 14 so that current of R, will be normal.

source of power -by means of the anti-resonant circuits.

cuits 15 and 15. These circuits, are made anti-resonant to the frequency produced by that fre'- quency Will not feed back into the repeater R, orinto the circuit of the rectifier 3.

The manner in which this circuit operates is as folloWsrLetit be assumed thatthe.

transmission characteristics of the line L, are such that the amplitude of the pilot channel atv theeoutput side of the repeater This voltage When impressed upon the grid of the rectifier 3 will cause a current to flow in the plate circuit of the'rectifier, which includes the Winding of relay 5, which will produce no effect upoh the armature of this relay. That is to say, the tension of the biasing spring of this armature is just suficient to equal the magnetic pullproduced by the normal curvrent flowing through the Winding of the relay. Consequently, the armature remains lf, on the'other hand,

less than normal to a predetermined extent, the armature of relay 5 would move and touch either its right or left-hand contact. This Would serve to connect the source of potential 7 with 8, which would notify the local repeater attendant, and it Would also'set in operation the apparatus for transmitting a signal lto the attendant at' the receiving terminal. station,v apprising him of the change in the transmission characteristics of ,the system. The current from the source 7 will simultaneously operate therelays 9 and 10. The operation of the former will connect the 11 Withthe motor 12 of the the lamp' coding commutator and also Will startin operation the oscillator 14. The operation of relay with the output of the oscillator 1 4. ,so that there will Vbe transmitted over the line L1 to the receiving terminal 16 at the distant end a series of impulses of the frequency produced by the oscillator 14, arranged in accordance `with the code `set up by the commutator 13. These coded impulses will be prevented from getting back into the repeater R, or tothe rectiierh3 e receiving terminal would include an alternating current relay that would serve to translate the trains of oscillations of the frequency produced by 14 into direct current impulses Which would operate a selecting device, preferably of .thetype used in train dispatching systems, which type is 10 vill connect the line L, direct'ly Abattery 24 l spectivelyz 'Wheatstone teeario disclosed in the patent to Field, No. 1,343,-

256, dated .lune 15, 1920.

The arrangement shown in Fig. 3 is a modification of that shown in Fig. 1, the

la series of impulses arranged in accordance with a code. The alarm circuit, which is bridged across the repeater R1, is tuned byv means of the condenser 2 and the primary Winding of the transformer 1 to the frequency of the pilot channel. The secondary Winding of this transformer, together With the condenser 4, also constitutes a tuned circuit which is connected With the grid of the tube 3, which constitutes one of the arms -of a Wheatstone bridge network. This tube is balanced by another tube 3 which is similar in structure and characteristics to tube 3.l The laments of both tubes are connected in series with each other and With the source of current 17 and the rheostat 18. Apotentiometer 19 and source of potential 20 are connected'in the grid circuit ofthe tube 3 which also includes the negative biasing vbattery 121. The source 53 applies the proper negativel bias to the grid of the tube 3. rThe equal'arms 22 and 23 constitute the ratio arms of the bridge.

is connected with the junction of the arms 22 and 23, which in turn are connected with plates of the tubes 3 and 3', re-

Bri-dged across opposite corners is a circuit including a.- galvanometer 25, a relay 26, and the windings of a contact volt# meter 27. together connected With the source of current 28 which also `is connected with the winding of the relay 29. The voltmeter is A source of platel The contacts of this voltmeter are so deslgned and ladjusted that Avvhen'the bridge is balanced the armature A-of the voltmeter will be at its midposition and the current How from the source 28 through the winding of relay 29 Wi'll not be shunted by the armature ofthe voltmeter 27. Relay 26 is of a sensitive .type thatreleases on zero current. Relay 30 is aI time relay which operates Whenever relay 26 operates. This time'relay serves to control a second time. relay 31 which controls the operationjof the code-transmitting re.- lay 32. 'A The latter relay is so=adjusted that whenever relay 31 operates, the arm 33 will begin to -move .over the contacts of the codesending device 34, which is adapted to transmit a series of impulses in accordance with a predetermined code. These impulses will operate relay 35 which opens the shunts relatie circuit and over the line Ll'lto the receiving?.

terminal station atthe distant end thereof. Whenever relay 35 operates to open the shunt, the anti-resonant circuits become op erative, and since these circuits are antiresonant to thepilot channel frequency, they .prevent the transmission of this frequency beyond the point Where the anti-resonant ycircuits are cut in. lt will therefore be seen that with the operation of relay 35 in accordance With the code set up upon the device 3d, the pilotchannel will vtlovv over the line L, to the receiving terminal station in a series of impulses representing a codesigf nal controlled by the device 34.

At the receiving terminal vstation the line la, is connected with a plurality of branches. @ne of these branches is tuned by the coudenser 36 and the primary Winding ontv the transformeri37 to be resonant to the pilot frequency. Another branch L2 eomprisesa plurality of band ilters by means of. which the carrier channels are separatedl and led into their respective terminal circuits: This latter feature forms no part of this invention and therefore will not be described in detail. The terminal circuit for the pilot channel resembles somewhatA the circuit at 4the repeater station. '.lhus the secondary ot, theV transformer 37 and the condenser 38 constit-ute a circuit tuned to the pilot frequency which is connected with the grid of the tube 39. rlhis input circuit also vincludes the negative biasing battery d() and the potentlometer ell. The corresponding arm ot'the bridge includes the `vacuum tube d2. The laments ot both tubes are in series yWith thel battery i3 and the rheostat 44:. The negative bias upon the grid ot the tube l2 is supplied by the batteryvll. 'lhe arms ll'and l? are connected with the plates ot the tubes 39 and 42, andthe junction ot these arms is connected with the source et plate voltage 48. Bridged acrossopposite cornersof' the arms is a circuit including the galvanometer e 49 and a relay 50.` 'llhis relay opens and `closes its contact Whenever an impulse et -current impressed upon the grid of the tube 39 causes variations inthe plate' current oil that tube. This relay controls'a pluralit ot selector relays, such as 51 .and 52, vv ich preferably are o f the type, used in trainl dispatching systems, that is disclosedin the patent to lField, No. 1,343,256, dated June 15, 1920. Each of these selectorswould, when operated, control a signal device which may be different in order` that the attendant would know by the^character of the signal which selector had operated. Thenumber of selector relays Aemploye-d would, of course, be,

equal to the number ol code-transmitting devices employed at the repeater points along the line.

The manner in which the system operates in order to carry'cut the invention isas tollows: Let it `be assumedv that the system is normal, so that the magnitude et the pilot channel current at the output side of the re,- peater R, is normal. This current will How over the line L, to the receiving terminal station and also into the branch at the repeater station lt and into similar branches at other repeaters. The current oWing' into this branch will impress a voltage upon the grid of the tube 3, which Will cause current of a known amount to tlow from the plate to the filament of this tube. This current is supplied by the source 2d. At the same time current from this source Hows through the plate circuit ot the tube 3. By adjusting 95 the. voltage of the biasing battery 553 connected with the tube 3*' the bridge may be balanced for the normal voltage impressed upon tube 3 by the ilotchannel. Consequently no current Will How inthe circuit including the galvanometer 25and the relays ,in series therewith. rllhe pilot channel current will dow in the circuit that includes the galvanometer 4:9 and the relay 50.- Censel quently'no signalv is given at the terminal station.

Let us assume thatl the pilotcbannel lrein5- quency voltage has increased to a predetermined"value ,due to 'changes in lineI conditions. ylhis voltage, when impressed upon the grid oit the tube 3, Will cause a space current to dow between the plate and 11G the filament ot this tube that is greater than normal. llhis dow et current `will unbalance the bridge and Will cause current to liow v through the galvanemeter 25, the-relay 26, and the conta-ctvoltmeter 27. Relay 26 115 will beenergized, Whichvvill in turn cause the operation of relay 30. 'llhecontact voltmeter `will likewise be energized te such'an extent that its armature will touch one el its contacts and thus will shunt a portion of 120 the current that normally would dow through the Winding of relay 29. e 'lhis'will allow relay 29 to release, thus establishing al circuit from .the battery 54', one ont the contacts' et relay 30, and the Winding of relay 3125 3l, energizing the latter. vCurrent will thereupon dow from the battery 55 through the-winding of relay 3,2to ound through the contact of relay 31.. This will cause the arm 33 of the code-transmittihg device 34 la normal, the

.representing a train of waves of the pilot frequency and of a magnitude greater than in accordance withthe code set up upon the device 34. These impulses will impress a voltage upon the grid of the tube 39 at the terminal station, which will cause current to flow from the plate to the filament ot' that tube, that is greater than normal. rl1 his will upset the balance of the Wheatstonebridge and cause impulses of direct current to flow through the circuit, including the galvanometer 49 and the-relay 50. vlllach impulse of direct current -corresponds to a train olf .Waves of the pilot frequency and of amplitude greater than normal impressed upon the grid'of the tube 39. Relay 50 will accordingly open and close its contact at the beginning and the end or each direct current impulse. 'lhis will cause the selectors 5l and 52 to bestepped around, but only that selector will be operated which is adjusted to respond to the group of impulses representing the code sent out by the pilot channel transmitting device at the repeater *Rr rlhe manner in which these selectors operate is clearly described in the patent to Field, heretofore referred to. Upon the operation of the selector, which will loe assumed to be 5l, the lamp and the bell connected with that selector will be energized. kThe attendant at the terminal station will thereupon know that the variation in the "line conditions that caused the increase in the amplitude of the pilot channel voltage lies beyond the repeater R1. He will thereupon call the repeater attendant at llt1 and also at the distant transmitting station and cause them to edect such adjustment as to llorinlg the transmission baclr to the desired eve In like manner, it the camplitude of the pilot channel voltage dropped to a predeter- ,mined extent below normal, the ilot channel code-transmitting device at t e repeater station would function and transmit a signal to the receiving terminal station.. lt will be seen that the contact voltmeter 27 at the repeater station has two contacts,- one ot vwhich touches the armature whenever the termined amount, an

oes upward a prede- `the other when it oes ldown a predetermined amount. The eiect upon the subsequent apparatus is the pilot channel voltage the winding of the' frequency. Accordtrains being separated by spaces alarm operated depending upon Lefranc `same regardless of the .character of the embodied fin particular forms, it is capable 1 of embodiment in other and different forms Without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a carrier signaling system, the

method which consists in transmitting over a line an alternating current constituting a pilot channel, selecting part of the pilot channel current at a point between the terminals of the line and effectively interrupting in accordance with a predetermined code the dow .of pilot current over the .said line whenever the said current exceeds a ixed limit, receiving the code interrupted current at another point upon said line nmore remote from' the transmitting end than the said selecting station, and operating an alarm responsive only to the code transmitted from a particular station.

2. ln a carrier signaling system, the method which consists in transmitting over a line an alternating current constituting a pilot channel, effectively interrupting in accordance with a predetermined code the How ot current over the said line whenever the said pilot current exceeds a Fixed limit, and

selectively operating at another point onsaid` a line an alternating current constituting a lOl) pilot channel, edectively interrupting in accordance with a predetermined code the iiow of pilot current over the said line when the said current at the point of interruption exceeds a rixed limit, the code ot interruption produced at one point beingdi'lferent from that produced at another point, and selectively operating by the said interrupted current an alarm at a supervisory station connected with the said line, the particular the code of interruption of the current.

4l. ln a carrier signaling system, the combination with a line olf a source ol.3 alternating current constitutmg a pilot channel connected with said line, a supervisory station connected with said line and a code transmitting station connected with the said line between the said sourceand the said supervisory station, the said code transmitting stationhaving means to interrupt the flow of pilot current over the said line in accordance with a predetermined code when the current at that station exceeds a fixed limit, the said receiving station having an alarm signal responsive only to the said codeinterrupted pilot current..

5. lin a carrier signaling system, the com- 'bination with a transmission circuit of a source of l alternating current connected therewith constituting a pilot channel, code transmitting means connected With the said transmission circuit comprising means responsive to predetermined variations from normal of the pilot current, a code transmitting device controlled by the said currentresponsive means, and means controlled by the code transmitting means to interrupt the transmission of the pilot current over the said line in accordance with the predetermined code, and an alarm signaling means connected with the said transmission circuit responsive rent. l

6. In a carrier signaling system, the comlbination with a transmission circuit of a transmission of the pilot current in accordance with the predetermined code, and a receiving circuit connected with the said transy mission circuit comprlsmg means to select to the impulses of the-pilot cur? the pilot current,and means responsive to the impulses ofsaid current to actuate an alarm signal. 7

In a carrier signaling system, th method which consists in transmitting over a line an alternating current constituting a pilot channel, selecting part of the pilot channel current at a point between the terminals ofthe line and effectively modulating the pilot current over the said line Whenever the said current exceeds a lixed limit, receiving the modulated Icurrent at another point upon said line more remote from the transmitting end than the said selecting station, and operating an alarm responsive only to the modulated current from a particular station.

8. In a carrier signaling system in which a pilot channel and a signaling channel are simultaneously transmitted, the method of determining the level at any point which consists in selecting a part of the pilot chanlnel current and using it to modulatethe re- ,mamder of the pilot current being transmitted 'over said system Whenever said current exceeds a fixed level.

In testimony whereof, I have signed my\ name to this specification this 17th day of September, 1926.

` HERMAN AFEL. 

